1. Field
The present invention relates to an optical signal processing system, and more particularly, to an optical source device capable of high-speed modulating and long-distance transmitting an input optical signal.
2. Discussion of Related Art
In general, an injection type broadband optical source does not require a control of a wavelength of an optical source of an optical transmitter, and a manufacturing process of the optical source is simple, compared to a Wavelength Division Multiplexing-Passive Optical Network (WDM-PON) method using a non-injection type optical source, such as a wavelength tunable laser. Further, the injection type broadband optical source is relatively easy to implement a system, and establishment cost thereof is low, compared to the wavelength tunable laser.
A Reflective Electro Absorption Modulator integrated with Semiconductor Optical Amplifier (REAM-SOA) is one of the injection type broadband optical sources. The REAM-SOA has a structure in which an Electro Absorption Modulator (EAM) is monolithic integrated with a Semiconductor Optical Amplifier (SOA). Accordingly, in the REAM-SOA, the amplification of the optical signal is performed by the SOA, and the modulation is performed by the EAM, thereby increasing a transmission rate to be 10 Gbps or more.
Since a 3 dB gain bandwidth of the SOA is over the wavelength of 50 nm, the SOA is operable in a wide wavelength range with uniform gain characteristics.
Unlikely, the modulation characteristics of EAM is strongly depends on the wavelength difference between the band gap of EAM and the operation wavelength, so that it is difficult to obtain a uniform extinction ratio, low optical loss, and a low chirp property in a wide wavelength band. Accordingly, the EAM has a characteristic in that an operation wavelength band is relatively narrower than that of the SOA, so that the REAM-SOA has difficulty in efficiently amplifying and modulating a high-speed optical signal in a wide operation wavelength band.
In order to solve the disadvantage, an optical device having the same function may be manufactured by integrating a Mach-Zehnder Interferometer (MZI), but the optical device integrated with the MZI has a complex process, a low yield, and a relatively long length compared to the EAM. Accordingly, the optical device integrated with the MZI is not appropriate as a small and low cost broadband optical source.
Further, the EAM may perform high-speed and long-distance transmission for an input power of a wide range. However, in the SOA, a noise problem is generated in a low input power, and a signal distortion is generated by gain saturation in a high input power, so that the SOA has an input power dynamic range in which an optical signal can transmit with low transmission power penalty. Accordingly, the REAM-SOA device may transmit an optical signal with a high speed only in a specific input power range.
Accordingly, as an optical communication system becomes have a high speed and a large capacity, there is necessity for a broadband optical source, which has a uniform gain characteristic, extinction ratio, and chirp characteristic for an injection signal of a wide wavelength band, and is capable of increasing a branching ratio for configuring a low price system or performing high-speed and long-distance transmission even in a low injection optical signal.